A new seismic site coefficient model is developed in this article from the results of over 48,000 total stress, 1D equivalent linear and nonlinear ground response simulations assuming conditions at seven locations in the South Carolina Coastal Plain. Site coefficients (F) computed from the simulations are plotted versus average shear‐wave velocity in the top 30 m (VS30) and grouped by location, spectral acceleration, and spectral period. In all plots, it can be seen that F increases from zero to a zone of peak values as VS30 increases from zero, and then F decreases to a value of 1 as VS30 approaches the reference soft‐rock value. Variables found to be most influential on F, in addition to VS30 and spectral acceleration, are stiffness of material in the top 100 m, depth to top of rock, and frequency content of the rock outcrop motion. A mathematical model for median values of F defined by these five variables is proposed. Significant differences exist between the new seismic site coefficient model and the site coefficients commonly assumed in current seismic design codes, particularly where VS30 is <180 m/s and where the top of the rock is at shallow depths. The new model is partially validated using data from the 1989 Loma Prieta earthquake. Because the new model is based on a broad range of soil/rock properties, it should be applicable to other areas with similar conditions and may be applicable in areas with different conditions if the model variables are appropriately calibrated or modified.